newton's third law
by milkandbone
Summary: in science, for every action, there is an equal and opposite reaction, and their love is everything in-between.


"Pluto will always be a planet in my room."

And she hasn't noticed it but he's good-looking, in a disheveled way. Messy hair. Long nose that _finally_ fits his face. Blue eyes. _Really_ blue eyes.

Her expression ripples with that same, vaguely sweet sort of understanding she always has. But her eyes widen a fraction — not enough to be telling, but enough to indicate that she's _fascinated_.

Her head tilts because she's looking at him, _really_ looking at him.

" _Good_."

###

"Did you always know you'd end up with mom?" she asks absently, tapping her fingers against a clean plate.

" _No_ , not really but—" Cory blusters, raking his fingers through his curly hair.

"Thanks," she interrupts, briskly putting down the last dish with a slight grin on her face.

###

Two months later they're in Farkle's bed.

They don't do much but talk. He asks her questions about the universe that he already knows and sometimes she reads him passages from outdated physic textbooks their parents read in high school.

Bethany Bird tries to help Riley with her stunts after school on Wednesdays so she can try out for the high school cheer team in the fall. The gymnasium is closer to Farkle's sky-high mansion than her apartment, so it just makes sense to spend the night there. Her parents don't think anything of it, he's Farkle.

He's _Farkle_.

Pluto is mile-high and silver-bright and Riley still has a problem finding it amongst all the other planets.

She continues to glare at his planetarium for a few moments longer until he carefully takes her hand and points to where her precious planet is. Riley doesn't like knowing where she stands in the world, and to her, pluto doesn't either. No one really knows where to pinpoint her, and not everyone can find Pluto so easily, except Farkle. Farkle just _knows_.

His hands are cold.

"I know." he mutters

She fidgets a little out of embarrassment — she didn't mean to ask out loud. She recovers quickly and leans into his personal space.

"You _know_?" she teases, smirking just wide enough that her cheeks become full. "Is there a scientific reason for cold hands?"

If it were any other girl but Riley, Farkle would think this was flirting — but it's Riley.

She's _Riley_.

She's Riley and he's still holding her hand.

Usually, he'd give her the scientific reason why his hands were so cold. He'd list off facts Maya would hit him for and Lucas would snooze off to. But Riley _listens_. He's slightly dehydrated and has low levels of iron from the amount of meat he _hasn_ _'_ _t_ been eating because of his mom's vegan phase.

Farkle is known for a lot of things, and distracted isn't one of them.

 _Usually_.

He's always been in love with Riley, but _this_ , whatever it is, is _different_. It was ridiculous that her freckles became another formula to diagram. He reaches up to brush the hair from her face and curls his toes into the smooth slate floor and ignores how uncomfortably tight his chest suddenly feels. Farkle doesn't know what he's doing — not really.

Everything is easier with Farkle she thinks. There is no stammering, and no second guesses. Lucas took her breath away to the point where she _suffocated_.

"Cold hands usually mean a warm heart."

With Farkle, breathing is easy, and she wonders if it should be.

She—she _giggles_ and he flushes a truly embarrassing shade of bright pink. Farkle can't stop the helpless half-smile that plays around the the corners of his mouth.

"I have to disagree." she says in dazed whisper, "Your hands are cold, because _mine_ are warm."

She kisses him before he has a chance to respond.

Two years after their first kiss, they have their second one.

###

"Did you hear that Farkle broke up with Smackle!?" Maya sing-yells as she shimmies in from Riley's door. "Dr. Farklestein and Isadora the Explorer are finished— right before graduation too! Kinda cold if you ask me since she had tickets to grad and all."

Riley is smiling, and it's a little dopey and a lot adorable.

###

They're not dating.

He doesn't even know what _they_ _'_ _re_ doing is called. Maybe they're too young, they probably are, but he feels like he's known Riley forever, and he has.

She doesn't know what she's doing — not really. Somehow, Maya managed to get some foreign french films with scenes too inappropriate for her to ever be watching. So she watches them anyways because this is the kind of bad influence Maya has that's harmless. Well, harmless for everyone but Riley apparently.

Because the moment when Riley slips her tongue into Farkle's mouth, it's bleeding from his teeth indentations.

"What are you trying to _do?_ " he asks, sounding horrified at what they both did.

She looks like a maniac smiling. Her front teeth are stained pink from the blood, and he would be grossed out but — _fuck._ She's smiling, she's always fucking smiling. This time it's a mischievous smile, the one he used to see when she schemed with Maya, but sees more often when she's kissing him. What does she even _see_ in him? What _she_ sees isn't what _he_ sees, but that's Riley Matthews for you. She lives on an entirely different universe, a whole other _dimension_ , because only something not of this world would even want to kiss him the way Riley does.

She explains to him the definition of a french kiss and he burrows his head into her hair. It smells like cinnamon rolls and oranges and he's reminded, suddenly, exactly why he's okay with going along with _this_.

She reached up and smoothed up his disheveled hair as she smiled. _"_ _So can we try it again?_ _"_

A question.

"State your hypothesis." his eyes are laden with sleep, and his hair is disheveled.

"You'll like it." she confirms sweetly.

"I'd like a bloody tongue touching mine?" he asks softly. She's leaning in with a satisfied smile upon her mouth.

"Not _a_ bloody tongue. _My_ bloody tongue. You have to test out my hypothesis, for the sake of science of course."

Farkle hesitates. Licks his lips. Tilts his head to the left. Considers the possibilities.

"Of course."

He tests out her hypothesis, analyzes his results and concludes that the taste of red copper from her tongue is surprisingly sweet.

He should feel bad because he doesn't deserve her.

He should feel bad.

He doesn't.

###

Lucas finds her doing summer reading in the library; a vague vestige of something they had, all things considered.

"You and Farkle?"

It's abrupt and kind of rude, but he assumes they're close enough to forget about formalities and he's right. Riley paused with the paper-thin page of her _To Kill a Mockingbird_ clutched between her thumb and forefinger. She waited a while before answering. And then—

"No," she says, careful to keep her hands steady as she resolutely flips the paige. "Not yet."

###

"Love is just a chemical reaction in your brain. It's serotonin. That's all _it_ is."

This is what Farkle says to Riley the first time she tells him — really tells him that she is in love with him. Because this isn't middle school, it's high school now where things actually matter.

He met her at half past midnight in the lobby of her apartment. It took the first second in his arms for her to tell him she loves him, and it took the next 29 minutes afterwards for him to comprehend it.

She used to believe love was something else too. She used to believe love was giving up your entire soul for another person. Riley realizes now that being in love is simple. It is loving someone, and loving yourself one thousand times over because of it.

"Riley." he finally whispers.

"Yes?" Riley answers, tilting her head to the side. He tucks a strand of her hair behind her ear and rubs his thumb along her jawline.

" _Are you mad at me?_ " he asks, halting her movements.

He can _feel_ the slow smile spread across her face.

"No," she replies, voice suddenly quiet on his neck. " _Because you_ _'_ _re wrong._ "

" _Really?_ " he counters quietly.

She slides her fingers along the crease at the top of his thigh.

He discovers in that hallway that love is a lot like her God and her kisses and her mouth and the way her hips fit _perfectly_ into the cradle of his lap, it is an experience that even science cannot explain.

"I love you Farkle."

"And I love you."

###

" _Farkle?_ " Maya hisses, lowering her voice and glaring when she notices the amount of customers at Topanga's are paying attention to them.

"Are you done?" Riley sighs, finally deigning to speak as she squirts her eggs with ketchup, Maya feels nauseous but her throat is too raw from her previous screams.

"Why didn't you tell me _sooner_? How does Huckleberry know _before_ me?" Maya grits out, nostrils flaring as she visibly fights off a scowl, Riley hums, semi-fondly.

"Lucas knew nothing, _officially_." she says sweetly, tilting her head "You're the first one to know that Farkle actually asked me out, isn't that enough?"

"It's the principal of the matter," she retorts, unable to help herself; her temper, she knows, is her least attractive quality. "I didn't even know you guys were talking!"

"Oh come on peaches, please don't be mad!" she coos.

"Fine," she says bluntly. "You just have to be completely honest now. How far have you guys _gone_?"

Riley swallows _hard_.

###

It is after Lucas' last football game of the season during their junior year when they finally have sex.

He looks at her, _observes_ her: catalogues every single detail, from the slope of her nose to every individual eyelash to the way she wraps her arms around her knees and tags down the sleeves of _his_ competitive math league sweatshirt.

It can get really cold in his room.

"Good morning," he says, breath moist against her neck.

She inhales sharply; he smells like clean linen and spearmint and apple cinnamon, and she isn't sure which scent is more intoxicating—but she's dizzy with it, whatever it is, and she registers her heartbeat skipping faster as his grip tightens around her arm.

"Good morning," she says, breathless. "Do you want to watch the sunrise?"

He presses his cheek into the curve of her back, hair mused and glasses askew because even 5 A.M is too early for him.

"Scientists don't watch the sunrise." he scoffs.

"Oh, yeah?" she grins sharply.

"They document it. They learn how it rises and why it has different shades of red, yellow and orange. They calculate its distance—"

She isn't surprised that they got to this point. If there's anything she learned from Farkle, it is that science is constantly changing. There is always new discoveries and past theories are always contradicting new findings — and she likes it. She likes that being with Farkle leaves something to be discovered, that they constantly evolve and change _together_.

"So you don't want to watch the sunrise," she pouts, arranging her legs on either side of his.

"No," he confirms, nudging her upright. "There are other things I'd like to document."

He thrusts up. She whimpers.

###


End file.
